Apple shipped 2.2 million units of the Watch in Q1, and Apple is by far the dominant player in the nascent market. But a growing field of rivals, building watches based on Google's Android Wear software and on the open-source Tizen system, is catching up.

Samsung is the number 2 player in the market, with 14.3% market share. A catch-all group of others have a combined market share of 33.3%, according to the report.

Apple released its smartwatch in April 2015. While some analysts and investors hoped the Watch would ignite a new consumer craze for wearable gadgets, the mainstream appeal of smartwatches and other wearables remains unclear. The Apple Watch has faced criticism of being slow and of having limited usefulness.

Apple, which does not disclose sales figures of the Watch, is expected to release a new version later this year that will include new features to address some of the perceived shortcomings.